Slot-gate foundry mold



Aug. 30, 1949- R. c HAWK ET AL 2,480,650

Patented Aug. 30, 1949 UNITED STATES OFFICE SLOT- GATE FOUNDRY MOLD Ralph C. Hawk, Bay County, and John G. Mezofi,

Bay City, Mich., assignors to The Dow Chemical Company, a corporation of Delaware Application June 13, 1946, Serial No. 676,379

Claims. 1

This invention relates to improved mold constructions and foundry procedures for making metal castings.

In making castings of many types, it is desirable that the molten metal be introduced into the foundry mold in such manner that the casting solidifies progressively from the bottom upward. In this way, each portion of the casting as it freezes is overlain with molten metal, and shrinkage flaws and porosity are largely avoided.

One means of achieving upward solidification which has been recommended is the slot-gate mold, sometimes termed slit-gate or knife-gate mold. In this construction, a deep inlet well is formed in the mold adjacent to the casting cavity and is connected to the latter by a narrow vertical slot which usually extends the full depth of the cavity. The metal to be cast is introduced into the well and from there passes through the slot into the cavity. It is intended that the metal flow wholly within the well until it reaches a level corresponding to that of the metal already in the casting cavity and then fiow gently through the slot-gate horizontally into the cavity, thus entering on top of earlier poured metal. In this way the newly added and hottest metal should always be at the highest point in the mold, so that upward freezing will be assured.

In practice, slot-gate molds of types heretofore known have been only partially effective in operating in the desired manner. In most instances, the metal being poured, instead of first flowing in the well to the prevailing metal level and thence into the cavity, tends to cut through the slot below the metal level and stream upward within the casting cavity, upsetting the thermal balance. Thus, in bottom-pour molds, in which the metal enters the well from below (British Patent 408,153), this effect is quite pronounced because the upper parts of the well are comparatively cold and retard the flow, whereas the submerged slot is hot and offers no such resistance. With top-pour molds (German Patent 670,316), a similar result often occurs, because the kinetic energy of the stream of metal being poured usually carries it below the level in the well and forces it through the slot near the bottom end. There is a, further effect in that even at ordinary pouring rates a part of the metal may spill through the slot at levels above the level in the cavity, causing splashing and turbulence. All these disadvantages are observed in some degree with center-pour slotgate molds (U. S. Patent 2,291,788)

With these considerations in mind, it is the principal object of the present invention to provide an improved slot-gate mold construction which in actuality achieves in large measure the desirable flow path for the metal being poured which has been intended in prior slot-gate molds. Another object is to provide a mold which is particularly adapted to the founding of magnesiumbase alloys and permits pouring sound heavy castings with, in general, less rigging than has been required heretofore. An additional object is to provide an improved procedure for filling slot-gate molds.

These objects are realized in the invention by positive means associated with the inlet well of the mold for insuring that the effective level at which the metal being poured passes through the slot-gate into the casting cavity is neither materially above nor below the level of the metal already in the cavity. These means may include an inlet orifice or other arrangement for controlling the entry of metal into the well, guides for regulating the type and direction of metal flow within the well, and a screen for controlling the movement of metal from the well into the casting cavity, as will be described.

According to the invention, the metal being poured into the inlet Well of a slot-gate mold should preferably enter as a stream having a cross-sectional area small relative to that of the well. In this way, there is little if any tendency for the well to run full to the top, so that spilling of metal through the upper portion of the slotgate is largely avoided. In addition, with the stream of relatively small area, the kinetic energy of the moving metal is not more than can be largely dissipated by impact with the body of metal in the well. Consequently, the stream has little tendency to force metal through the slotgate below the prevailing metal level.

It is of course possible to limit the size of the stream entering the well by careful handling of the ladle or pumping system from which the metal is poured. It is preferable, however, to inset in the mold an inlet member having therein a restricted orifice opening into the top of the well, the cross-sectioinal area of the orifice being small relative to that of the well, i. e. the diameter of the orifice being a minor fraction of that of the well. The orifice functions as a choke to limit and maintain constant the cross-sectional area of the entering stream, thus eliminating the need for extreme care in the pouring and yet insuring a smooth, controlled flow of metal into the well.

In the slot-gate molds of the present invention, it is desirable to provide one or more guides Within the inlet well for conveying any stream of molten metal downwardly inside the well without substantial splashing. Guiding wire, either a loose bundle of parallel wires or a strand of steel wool, down which the metal can run as a thick film, much as water follows down a rod, is most satisfactory.

By providing a fixed path on which the entering metal can flow, the guide serves to carry the metal down to the level of the body of. metal: in the well without any tendency to splash or spill through the top of the slot-gate- The guide also acts to break the fall of the metal and to prevent turbulence, so that the flowing metal enters the body of metal already in the well. withoutrexcessive agitation or surging and passes smoothly through the slot-gate at the prevailing metal level. Further, according tothe invention, it is'highly advantageous to place a screen or other multiplyperforated baille in the inlet well or a slot-gate mold and covering the entrance to the slot-gate. Ama'j'or purpose of sucha screen is to stabilize the how of metal from the well into the casting cavity. By momentarily impeding the metal and requiring it to pass through a large number of small openings, the screen efiectively reduces eddying in the stream, permitting quiet flow into thec'asting cavity. The screen may also act as an additional guide, preventing splashing of metal through the upper part of the slot gate; While simple sheet screens may be employed, preferred construction calls for a tubular screen centered in the well, having a diameter which is'ama-jor fraction of that of the well, and extending it full depth;

In the founding of readily-oxidizable' metals, such as magnesium-base alloys, the screen performs the additional function of skimming unavoidableoxide inclusions from the metal as it enters the casting cavity. Unlike screens used heretofore; a screen within the inlet well has the advantage-that, since themetal level is constantly rising during pouring, a fresh screen surface is continually presented to the flowing metal; A further advantage of the'scr'een accordingto the invention is that possible plugging by theoxide filteredout takes place from the bottom: of the well'upward, andthisplugging assists in restraining flow'of entering metal into the casting cavity at levels below that prevailing in the well.

While the inlet orifice, guide wire, and screenas described are individually helpful in establishing the desirable flow path of metal entering a slot-gate mold, molds including combinations of these elements are-especiaiiyeiiective; A parties ula'rly desirable construction, which" illustrates a preferred embodiment of the" invention; i'sshown' in the accompanying drawing; in which Fig. l is a fragmentary vertical section of a slbt-gatemold, taken along the line i-l ofFig; 2; and

' Fig; 2' is a horizontal section of the mold, along the line 2-2 of Fig. 1.

Ihe mold shown in the drawing ismadeaconventicnal three-part mold or. rammed foundry sand 3' defining a casting cavity 5. A vertical inlet well 5 isforme'd in the mold adjacent to the casting cavity and extending the full. depth thereof, with a slot-gate 6 connecting, the well with the cavity. Held centered in the well by means of an inset sand core I at the bottom a tubular screen 8, made of sheet iron having 9.

very large number of closely-spaced small perforations and rolled and crimped into a tube of a diameter more than half that of the well. Optionally, the screen may be of woven wire fabric. Inset in the mold above the well 5 is an inlet core 9 having therein an orifice ID opening centrally into the top of the well above the screen, the diameter of the orifice being considerably less than half that of the well. A recess H is formed in the under side of the inlet core to receive the top portion of the screen 8. A strand of steel Wool l2 is disposed axially in the well, being tucked under the screenil at the bottom and extending through. the orifice I9 at the top. The mold is filled. from a pouring cup [3 from which a sprue it leads to the inlet core 9.

In using the mold of Figs. 1 and 2, the molten metal to be cast is poured into the cup l3 at a rate sufilcient to keep it nearly full. It passes through the sprue I l and the orifice H as a stream of constant rate inside thescreen' 8; This stream follows down the wires of the steel wool'within the screen to the level of the body of metal which has already entered. On reaching this level, themetal spreads out horizontally without turbulence and flows gently through the screen 8 and slot-gate 6' into the casting cavity 4. 7

While the invention has been described with reference to an inlet well having a" single slotgate, it is; equally possible to have two ormcre slot-gates opening from a single well and leading to the same or different casting cavities. It will alsobe appreciated that the principles of this invention are" as applicable: in plaster and" in'permanent-mold casting as in sand-casting.

The foregoing description i's-ill'ustrative rather than strictly limitative, there bein'g'manypossible variations of the construction described within thescopeof the following claims:

What is claimed is? l. A foundry mold having a castingcavity. an inlet well adjacent to the cavity, a 'sl'otL-g'at'e' connecting the cavity with. the well, an inlet member having an orifice therein leading into thetop of the well, the cross se'ction'al area of the-orifice being less than one-fourth that of the well, a tubular screen placed in the well under the orifice, and aguide'within the screen for conveying any stream of molten metal entering through the orifice downwardly'inside the screen without substantial splashing.

2. A foundry mold having a casting cavity, a vertical inlet well adjacentto the cavity, a'slotgate'c'onn'ecting the cavity with the well, aninle't core having an orifice opening. into the top of thewelLthe diameter of the orifi'cebei'n'g. a 'minor fraction of that or" the well, a tubular metal screen, the diameter of which ismore thanonehalf that of the well, placed in thewelllunder' theorifi'ce and extending the entire depth ofth'e well, and guiding wires disposed axially within the screen below the orifice for conveying any stream of metal entering through the orifice downwardly without substantial splashing;

3. The combination according to claim 2 where-'- in the guiding wires are in't'he form of a strand: of steel wool.

a. A foundry mold. having a. casting cavity; an inletwell adjacent tothe cavity,.a slot-gate connecting the cavity with the well, a tubular screen in the well extending the "full depth there' of, and guiding wirewithin the screen for conveying any stream of molten metal poured therein downwardly without substantial splashing;

5. A foundry mold 'havinga castingcavity, a

vertical inlet well adjacent to the cavity, a slotgate connecting the cavity with the well, a tubular iron screen, the diameter of which is more than one-half that of the well, placed in the well and extending the full depth thereof, and a strand of steel wool centered axially in the screen.

RALPH C. HAWK.

JOHN G. MEZOFF.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 261,999 Case Aug. 1, 1883 1,103,039 Cudell July 14, 1914 Number Number OTHER REFERENCES Non Ferrous Foundry Practice, by Lalng and Rolfe, Third edition (1943), page 168. 

